Kidney Infection: Symptoms, Same-Day Warning Signs, and Who Is at Higher Risk

A kidney infection is a painful type of urinary tract infection (UTI) that can affect one or both kidneys [1]. It is also called pyelonephritis [2]. It often begins in your bladder and moves into one or both of your kidneys [3], and it is more serious than a regular UTI and needs medical treatment [4]. If you think you have a kidney infection, see a health care professional right away [5].

How a Kidney Infection Starts

Bacteria from the skin or rectum can travel up the urethra and cause a bladder infection [6]. Most kidney infections are caused by bacteria or viruses that first infect the lower urinary tract, usually the bladder, and then move up the ureters to one or both kidneys [2]. A bladder infection that is not treated, or does not go away, can spread to one or both kidneys [7].

A bladder infection is not the only route. Cystitis, another type of UTI, is often the cause, but you can also get a kidney infection without having cystitis [1]. In some cases, your blood may carry harmful bacteria or viruses from another part of your body to your kidneys, and rarely, you might get a kidney infection after surgery [7].

That is why a bladder infection deserves attention early. If you have symptoms of a bladder infection, see a health care professional, as you may need treatment to stop the infection spreading to your kidneys [2].

Symptoms of a Kidney Infection

Symptoms can include fever or a high temperature, pain in your back or side, and nausea, feeling sick or vomiting [1][4][6][7]. The fever can be high, usually over 38C [4], and can come with chills [6][7]. Symptoms vary by age [7], and other symptoms can include:

• pain when you pee [1][4][7], or a burning or stinging feeling [1]
• needing to pee often [1][4][7]
• dark or cloudy pee [1][7], or pee that is bloody or foul-smelling [7]
• pain in your groin [7]
• diarrhoea [1]
• aching muscles and flu-like symptoms [1]

The symptoms may be similar to those of other UTIs, such as cystitis [1].

Babies and Young Children

Young children may also wet the bed or themselves, or be drowsy [1]. A child under 2 may only have a high temperature [1][7], and may also show signs of feeding difficulty and poor weight gain [7].

When to Get Help the Same Day

In the UK

The NHS advises: "Ask for an urgent GP appointment or get help from NHS 111 if:" "You think you or your child may have a kidney infection and:" [1]

• have a very high temperature, or feel hot, cold or shivery
• have a very low temperature below 36C
• have pain in the lower tummy or in the back, just under the ribs
• have blood in your pee
• are feeling or being sick
• have not had a pee all day
• you are pregnant

The NHS warns: "A kidney infection can be serious if it's not treated as it can cause sepsis." It also advises: "Call 111 or get help from 111 online if you cannot speak to or see a GP, or your symptoms are getting worse." [1]

The NHS says: "Call 999 or go to A&E now if:" [1]

• you are confused, drowsy or have difficulty speaking

The NHS also advises: "Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance." Bring any medicines you take with you [1].

In the US

The US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) advises: "Seek care right away if you have kidney infection symptoms. Although uncommon, a kidney infection could lead to sepsis, which can be life threatening." [7] Symptoms of sepsis may include [7]:

• fever and chills
• confusion
• rapid breathing and heart rate
• severe pain or discomfort
• shortness of breath

For a urinary tract infection that is already being treated, the US Agency for Healthcare Research and Quality (AHRQ) advises that if your symptoms are not getting better, or if at any point you develop fever, chills, back pain or vomiting, or feel more ill, you should seek an in-person appointment or "go to the emergency department" [8].

Who Is More Likely to Get a Kidney Infection

You are more likely to develop a kidney infection if you [2]:

• are female
• have a current or recent bladder infection
• are pregnant
• have a urinary tract blockage, such as a kidney stone or enlarged prostate
• have a urinary tract problem such as vesicoureteral reflux, which is more common in children
• have diabetes or problems with your immune system
• have a spinal cord injury or nerve damage around the bladder
• have trouble emptying your bladder completely, called urinary retention

Having a problem with your kidney, such as kidney stones, or having certain conditions or a weakened immune system may also make a kidney infection more likely [1]. UTIs and kidney infections are more common in women, but anyone can get one [1].

Possible Complications

When diagnosed early and treated properly, most kidney infections do not lead to complications [2]. In rare cases, they may cause [2]:

• high blood pressure
• kidney failure
• kidney scarring, which can lead to chronic kidney disease
• sepsis

Left untreated, a kidney infection can cause serious problems, such as damage to the kidneys or sepsis (blood poisoning) [4].

Who Is More Likely to Have Complications

Your chance of a complication is slightly greater if you [2]:

• are male
• are older or frail due to weakened strength or other problems of aging
• are pregnant
• have a problem with the structure of your urinary tract
• have had repeat kidney infections
• have certain health conditions, such as diabetes, kidney disease, or sickle cell disease
• have a weakened immune system or have had an organ transplant

Kidney Infection During Pregnancy

Kidney infections are more common in females than males and are common during pregnancy [2]. In the UK, being pregnant with a suspected kidney infection is a reason to ask for an urgent GP appointment or get help from NHS 111 [1].

How a Kidney Infection Is Diagnosed

If a GP thinks you have a kidney infection, you'll have your pee tested to check [1]. Health care professionals use your medical history, a physical exam, and lab and imaging tests to make the diagnosis, and will ask whether you have a history of health conditions that make a kidney infection more likely [9]. Tests may include [9]:

• urinalysis and urine culture
• blood tests, which look for serious infections, such as kidney infections, and may also show how well your kidneys are working
• one or more imaging tests: a computed tomography (CT) scan, magnetic resonance imaging (MRI), a radionuclide scan or an ultrasound

If you are male, the exam may include a digital rectal examination (DRE) to check for a swollen or enlarged prostate [9].

Treatment and Recovery

Treatment for a kidney infection may be given by a GP or, for some people, in hospital [1]. If you have a long-term health condition or you are pregnant, you may need to go to hospital for treatment [1]. If you are very sick from the infection, you may go to hospital, where a health care professional may give you IV fluids [5]. In the UK, most people treated in hospital are well enough to go home after 3 to 7 days [1].

Sometimes a urinary tract blockage, such as a kidney stone or an enlarged prostate, can cause a kidney infection, and you may need surgery or another procedure to treat the blockage [5].

You'll usually feel better after about 2 weeks, although people who are older or have underlying conditions may take longer to recover [1].

Things That Can Help While You Are Being Treated

While you are having treatment, there are some things you can try to ease the symptoms, and they can also help prevent a kidney infection coming back. These include [1]:

• rest: it can take up to 2 weeks before you feel able to return to work
• drink lots of fluids, such as water or squash: take small sips if you feel sick
• ask your doctor how much fluid you can drink if you have kidney problems
• always try to fully empty your bladder when you pee
• do not hold your pee in if you feel the urge to go

If Symptoms Linger or Come Back

In the UK, see a GP if you or your child have kidney infection symptoms that have not gone away after treatment [1]. If your symptoms return after you've completed treatment, see your health care professional right away [5]. Contact your health care professional, too, if an infection seems to be getting worse [5].

Conclusion

If a bladder infection seems to be getting worse, contact your health care professional, and if you have kidney infection symptoms such as a fever with pain in your back or side, seek care right away. After treatment, notice whether your symptoms fully clear. If they linger or come back, go back to your GP or health care professional, keeping in mind that recovery can take longer for older people and those with other health conditions.

Medical Disclaimer

This article is for general information and does not replace advice from a qualified health professional. If you think you need urgent medical care, get emergency help straight away.